SeamFramework.orgCommunity Documentation
By including the Seam 3 Servlet module in your web application (and performing the necessary listener configuration for pre-Servlet 3.0 environments) you will also have the servlet lifecycle events propagated to the CDI event bridge so you can observe them in your beans. Seam Servlet also fires some additional lifecycle events not offered by the Servlet API, such as when the response is initialized and destroyed.
These events correspond to the javax.servlet.ServletContextListener
interface. The event
object fired is a javax.servlet.ServletContext
(since that's the only relevant information
in the javax.servlet.ServletContextEvent
object). There are two qualifiers available that
can be used for selecting the lifecycle phase of the servlet context (initialize or destroy).
Qualifier | Description |
---|---|
@Initialized | Qualifies the creation event |
@Destroyed | Qualifies the destruction event |
If you want to listen to both lifecycle events, leave out the qualifiers:
public void observeServletContext(@Observes ServletContext ctx) {
// Do something with the "servlet context" object
}
If you are interested in only a particular one, use a qualifer:
public void observeServletContextInitialized(@Observes @Initialized ServletContext ctx) {
// Do something with the "servlet context" object upon initialization
}
The name of the observer method is insignificant.
The ServletContext
initialized event provides an excellent opportunity to perform startup
logic as an alterative to using an EJB 3.1 startup singleton. Even better, you can configure the bean to be
destroyed immediately following the initialization routine by leaving it as dependent scoped (dependent-scoped
observers only live for the duration of the observe method invocation).
Here's an example of entering seed data into the database in a development environment (as indicated by a
stereotype annotation named @Development
).
@Stateless
@Development
public class SeedDataImporter {
@PersistenceContext
private EntityManager em;
public void loadData(@Observes @Initialized ServletContext ctx) {
em.persist(new Product(1, "Black Hole", 100.0));
}
}
If you'd rather not tie yourself to the Servlet API, you can observe the WebApplication
rather than the ServletContext
. WebApplication
is a informational object
provided by Seam Servlet that holds select information about the ServletContext
such as the
application name, context path, server info and start time.
public void loadData(@Observes @Initialized WebApplication webapp) {
...
}
You can also use WebApplication
with the @Destroyed
qualifier to be
notified when the web application is stopped.
These events correspond to the javax.servlet.ServletRequestListener
interface. The event
object fired is a javax.servlet.ServletRequest
(since that's the only relevant information
in the javax.servlet.ServletRequestEvent
object. There are two qualifiers available that can
be used for selecting the lifecycle phase of the request (initialize or destroy) and one to filter the observer
based on the servlet path.
Qualifier | Description |
---|---|
@Initialized | Qualifies the initialization event |
@Destroyed | Qualifies the destruction event |
@Path | Qualifies the servlet path of the request (no leading slash) |
If you want to listen to both lifecycle events, leave out the qualifiers.
public void observeRequest(@Observes ServletRequest request) {
// Do something with the servlet "request" object
}
If you are interested in only a particular one, use a qualifer
public void observeRequestInitialized(@Observes @Initialized ServletRequest request) {
// Do something with the servlet "request" object upon initialization
}
You can also listen specifically for a javax.servlet.http.HttpServletRequest
simply by changing the expected event type.
public void observeRequestInitialized(@Observes @Initialized HttpServletRequest request) {
// Do something with the HTTP servlet "request" object upon initialization
}
You can associate an observer with a particular servlet request path (exact match, dropping the leading slash).
public void observeRequestInitialized(@Observes @Initialized @Path("offer") HttpServletRequest request) {
// Do something with the HTTP servlet "request" object upon initialization
// only when servlet path /offer is requested
}
The name of the observer method is insignificant.
The Servlet API does not provide a listener for accessing the lifecycle of a response. Therefore, Seam Servlet
simulates a response lifecycle listener using CDI events. These events parallel those provided by the
javax.servlet.ServletRequestListener
inteface. The event object fired is a
javax.servlet.ServletResponse
. There are two qualifiers available that can be used for
selecting the lifecycle phase of the response (initialize or destroy) and one to filter the observer based on
the servlet path.
Qualifier | Description |
---|---|
@Initialized | Qualifies the initialization event |
@Destroyed | Qualifies the destruction event |
@Path | Qualifies the servlet path of the request (no leading slash) |
If you want to listen to both lifecycle events, leave out the qualifiers.
public void observeResponse(@Observes ServletResponse response) {
// Do something with the servlet "response" object
}
If you are interested in only a particular one, use a qualifer
public void observeResponseInitialized(@Observes @Initialized ServletResponse response) {
// Do something with the servlet "response" object upon initialization
}
You can also listen specifically for a javax.servlet.http.HttpServletResponse
simply by changing the expected event type.
public void observeResponseInitialized(@Observes @Initialized HttpServletResponse response) {
// Do something with the HTTP servlet "response" object upon initialization
}
If you need access to the ServletRequest
and/or the ServletContext
objects at the same time, you can simply add them as parameters to the observer methods. For instance, let's
assume you want to manually set the character encoding of the request and response.
public void setupEncoding(@Observes @Initialized ServletResponse res, ServletRequest req) throws Exception {
if (this.override || req.getCharacterEncoding() == null) {
req.setCharacterEncoding(encoding);
if (override) {
res.setCharacterEncoding(encoding);
}
}
}
The name of the observer method is insignificant.
If the response is committed by one of the observers, the request will not be sent to the target Servlet and the filter chain is skipped.
Rather than having to observe the request and response as separate events, or include the request object as an
parameter on a response observer, it would be convenient to be able to observe them as a pair. That's why Seam
Servlet fires an synthetic lifecycle event for the wrapper type ServletRequestContext
. The
ServletRequestContext
holds the ServletRequest
and the
ServletResponse
objects, and also provides access to the ServletContext
.
There are two qualifiers available that can be used for selecting the lifecycle phase of the request context
(initialize or destroy) and one to filter the observer based on the servlet path.
Qualifier | Description |
---|---|
@Initialized | Qualifies the initialization event |
@Destroyed | Qualifies the destruction event |
@Path | Qualifies the servlet path of the request (no leading slash) |
Let's revisit the character encoding observer and examine how it can be simplified by this event:
public void setupEncoding(@Observes @Initialized ServletRequestContext ctx) throws Exception {
if (this.override || ctx.getRequest().getCharacterEncoding() == null) {
ctx.getRequest().setCharacterEncoding(encoding);
if (override) {
ctx.getResponse().setCharacterEncoding(encoding);
}
}
}
You can also observe the HttpServletRequestContext
to be notified only on HTTP requests.
If the response is committed by one of the observers, the request will not be sent to the target Servlet and the filter chain is skipped.
Since observers that have access to the response can commit it, an HttpServletRequestContext
observer that receives the initialized event can effectively work as a filter or even a Servlet. Let's consider
a primitive welcome page filter that redirects visitors to the start page:
public void redirectToStartPage(@Observes @Path("") @Initialized HttpServletRequestContext ctx)
throws Exception {
String startPage = ctx.getResponse().encodeRedirectURL(ctx.getContextPath() + "/start.jsf");
ctx.getResponse().sendRedirect(startPage);
}
Now you never have to write a Servlet listener, Servlet or Filter again!
These events correspond to the javax.servlet.HttpSessionListener
interface. The event object
fired is a javax.servlet.http.HttpSession
(since that's the only relevant information in the
javax.servlet.http.HttpSessionEvent
object). There are two qualifiers available that can be
used for selecting the lifecycle phase of the session (initialize or destroy).
Qualifier | Description |
---|---|
@Initialized | Qualifies the creation event |
@Destroyed | Qualifies the destruction event |
If you want to listen to both lifecycle events, leave out the qualifiers. Note that omitting all qualifiers
will observe all events with a HttpSession
as event object.
public void observeSession(@Observes HttpSession session) {
// Do something with the "session" object
}
If you are interested in only a particular one, use a qualifer
public void observeSessionInitialized(@Observes @Initialized HttpSession session) {
// Do something with the "session" object upon being initialized
}
The name of the observer method is insignificant.
These events correspond to the
javax.servlet.HttpSessionActivationListener
interface. The event object
fired is a javax.servlet.http.HttpSession
(since that's the only relevant
information in the javax.servlet.http.HttpSessionEvent
object). There
are two qualifiers available that can be used for selecting the activation or passivation
of the session.
Qualifier | Description |
---|---|
@DidActivate | Qualifies the activation event |
@WillPassivate | Qualifies the passivation event |
If you want to listen to both lifecycle events, leave out the qualifiers. Note that omitting all qualifiers will
observe all events with a HttpSession
as event object.
public void observeSession(@Observes HttpSession session) {
// Do something with the "session" object
}
If you are interested in only a particular one, use a qualifer
public void observeSessionCreated(@Observes @WillPassivate HttpSession session) {
// Do something with the "session" object when it's being passivated
}
The name of the observer method is insignificant.